The present invention relates to a new class of metallocene compounds, to a catalyst for the polymerization of olefins containing them and to a polymerization process carried out in the presence of said catalyst. The invention also relates to the corresponding ligands useful as intermediates in the synthesis of said metallocene compounds, as well as to processes for preparing said ligands and said metallocene compounds.
Metallocene compounds with two cyclopentadienyl groups are known as catalyst components for the polymerization of olefins. European Patent 129,368, for instance, describes a catalyst system for the polymerization of olefins comprising (a) a biscyclopentadienyl coordination complex with a transition metal and (b) an alumoxane. The two cyclopentadienyl groups can be linked by a divalent group.
More recently, heterocyclic metallocene compounds used in the polymerization of alpha-olefins have been described. For example, U.S. Pat. No. 5,489,659 relates to a class of silicon-containing metallocene compounds for the polymerization of alpha-olefins wherein the silicon atom is part of a non-aromatic ring condensed to the cyclopentadienyl ring. Metallocenes of this type are used in the polymerization of propylene. The activity of these metallocene-based catalysts is not satisfactory.
In International application WO 98/22486 it is described a class of metallocenes containing a cyclopentadienyl radical directly coordinating the central metal atom, to which are fused one or more rings containing at least one heteroatom. These metallocenes, in combination with a suitable cocatalyst, are used in the polymerization of olefins, such as propylene. However, the molecular weights that can be obtained at polymerization temperatures of industrial interest are still too low for most utilization and the activity of those catalyst systems, when used in the polymerization of propylene, is not satisfactory.
It would be desirable to provide a novel class of metallocenes which, when used in catalysts for the polymerization of olefins, in particular of propylene, have high activity such that the amount of the catalyst remaining in the formed polymer is minimized. Furthermore high-activity catalyst capable of yielding polymers endowed with high molecular weight, narrow molecular weight distribution as well as a high degree of isotacticity and thus of crystallinity would be desirable.
A novel class of metallocene compounds has now been unexpectedly found, which achieves the above and other results.
According to a first aspect, the present invention provides a metallocene compound of the general formula (I): 
wherein
Y is a moiety of formula (II) 
xe2x80x83wherein
A, B and D, same or different from each other, are selected from an element of the groups 14 to 16 of the Periodic Table of the Elements (new IUPAC version), with the exclusion of nitrogen and oxygen;
R1, R2, R3, R4 and R5, same or different from each other, are selected from hydrogen, a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl, C7-C20-arylalkyl radical, optionally containing heteroatoms belonging to groups 13-17 of the Periodic Table of the Elements; wherein two R3 can form a ring comprising 4 to 8 atoms, or R3 and R4 can form a ring comprising 4 to 8 atoms, which can bear substituents; with the proviso that when s is 0 or when R3 is hydrogen, R2 is not hydrogen;
m, n and s, equal to or different from each other, are selected from 0, 1 and 2;
m, n and s being 0 when respectively A, B and D are selected from an element of the group 16 of the Periodic Table of the Elements (new IUPAC version);
m, n and s being 1 when respectively A, B and D are selected from an element of the group 15 of the Periodic Table of the Elements (new IUPAC version);
m, n and s being 1 or 2 when respectively A, B and D are selected from an element of the group 14 of the Periodic Table of the Elements (new IUPAC version);
and wherein the ring containing A, B and D can have double bonds in any of the allowed positions, having an aromatic character;
Z is selected from a moiety of formula (II) as described above and from a moiety of formula (III): 
xe2x80x83wherein R6, R7, R8 and R9, same or different from each other, are selected from hydrogen, a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl, C7-C20-arylalkyl radical, optionally containing heteroatoms belonging to groups 13-17 of the Periodic Table of the Elements, R7 being different from hydrogen; optionally R6 and R7 or R7 and R8 can form a ring comprising 4 to 8 carbon atoms, which can bear substituents;
and when Z is a moiety of formula (II), Y and Z can be the same or different from each other;
L is a divalent bridging group; preferably selected from the group consisting of C1-C20 alkylidene, C3-C20 cycloalkylidene, C6-C20 arylidene, C7-C20 alkylarylidene, C7-C20 arylalkylidene optionally containing heteroatoms belonging to groups 13-17 of the Periodic Table of the Elements and silylidene containing up to 5 silicon atoms such as SiMe2, SiP2, SiMe2SiMe2 radical;
M is an atom of a transition metal selected from those belonging to group 3, 4, 5, 6 or to the lanthanide or actinide groups in the Periodic Table of the Elements (new IUPAC version),
X, same or different, is a hydrogen atom, a halogen atom, a R10, OR10, OSO2CF3, OCOR10, SR10, NR102 or PR102 group, wherein the substituents R10 are selected from the group consisting of C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radical, optionally containing heteroatoms belonging to groups 13-17 of the Periodic Table of the Elements;
p is an integer of from 0 to 3, preferably from 1 to 3, being equal to the oxidation state of the metal M minus 2, preferably p is 2;
The transition metal M is preferably titanium, zirconium or hafnium. More preferably it is zirconium;
Preferably the substituents X are chlorine atoms, methyl groups or benzyl groups.
Preferably the divalent bridging group L is  greater than Si(R17)2 or  greater than C(R17)2, wherein R17, equal or different from each other, are selected from hydrogen, a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl, C7-C20-arylalkyl radical, optionally containing heteroatoms belonging to groups 13-17 of the Periodic Table of the Elements; and wherein two R17 can form a cycle comprising from 3 to 8 atoms, that can bear substituents.
More preferably the divalent bridging group L is selected from the group consisting of  greater than Si(CH3)2,  greater than Si(C6H5)2,  greater than CH2 and  greater than C(CH3)2.
Preferably A is selected from sulfur, selenium, tellurium and polonium, more preferably it is sulfur.
Preferably B and D are selected from the group 14 of the Periodic Table of the Elements (new IUPAC version), more preferably they are carbon atoms.
When Z is a moiety of formula (III) it is preferably selected among those of formula (IV): 
wherein
R11, R12, R13, R14, R15 and R16, same or different from each other, are selected from hydrogen, a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl, C7-C20-arylalkyl radical, optionally containing heteroatoms belonging to groups 13-17 of the Periodic Table of the Elements, optionally R11 and R12, or R12 and R13, or R13 and R14 can form a ring comprising 4 to 8 atoms which can bear substituents. Preferably R14 and R16 are different from hydrogen. More preferably R14 is a C6-C20-aryl group, such as a phenyl or naphtyl group, and R16 is a C1-C20-alkyl group, such as a methyl group.
Non limiting examples of the metallocenes of the present invention are:
dimethylsilandiylbis-6-(3-methylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(4-methylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(4-isopropylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(4-ter-butylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-isopropylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-thiophene]zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-thiophene]zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-thiophene]zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,4,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-methylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-isopropylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-silole]zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-silole]zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-silole]zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-methylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-isopropylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-tellurophene]zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-tellurophene]zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-tellurophene]zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-methylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-isopropylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-tellurophene]zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-tellurophene]zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-tellurophene]zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diter-3-butyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-methylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-isopropylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-phosphole]zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-phosphole]zirconium dichloride and methyl;
dimethylsilandiylbis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-phosphole]zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
dimethylsilyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
isopropylidenebis-6-(3-methylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
isopropylidenebis-6-(3-isopropylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
isopropylidenebis-6-(3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-thiophene]zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-thiophene]zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-thiophene]zirconium dichloride and methyl;
isopropylidenebis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
isopropylidenebis-6-(3-methylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
isopropylidenebis-6-(3-isopropylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
isopropylidenebis-6-(3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-silole]zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-silole]zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-silole]zirconium dichloride and methyl;
isopropylidenebis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
isopropylidenebis-6-(3-methylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(3-isopropylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-tellurophene]zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-tellurophene]zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-tellurophene]zirconium dichloride and methyl;
isopropylidenebis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(3-methylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(3-isopropylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-tellurophene]zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-tellurophene]zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-tellurophene]zirconium dichloride and methyl;
isopropylidenebis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)zirconium dichloride and methyl;
isopropylidenebis-6-(3-methylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
isopropylidenebis-6-(3-isopropylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
isopropylidenebis-6-(3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-phosphole]zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-phosphole]zirconium dichloride and methyl;
isopropylidenebis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-phosphole]zirconium dichloride and methyl;
isopropylidenebis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
isopropylidenebis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2-methylcyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2-isopropylcyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2-phenylcyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2,4-methyl-cyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-5-[(2-methylphenyl)methylcyclopentadienyl-[c]-thiophene]zirconium dichloride and methyl;
dimethylsilandiylbis-5-[2-(2,4,6-trimethylphenyl)cyclopentadienyl-[c]-thiophene]zirconium dichloride and methyl;
dimethylsilandiylbis-5-[2-mesitylene-4-methylcyclopentadienyl-[c]-thiophene]zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2,4-diisopropyl-cyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2,4-diter-butyl-cyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2,4-ditrimethylsilyl-cyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2-methylcyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2-isopropylcyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2-phenylcyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2,4-dimethyl-cyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-5-[(2-methylphenyl)-4-methylcyclopentadienyl-[c]-phosphole]zirconium dichloride and methyl;
dimethylsilandiylbis-5-[2-(2,4,6-trimethylphenyl)cyclopentadienyl-[c]-phosphole]zirconium dichloride and methyl;
dimethylsilandiylbis-5-[2-mesitylene-4-methylcyclopentadienyl-[c]-phosphole]zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2,4-diisopropyl-cyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2,4-diter-butyl-cyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2,4-ditrimethylsilyl-cyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2-methylcyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2-isopropylcyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2-phenylcyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2,4-dimethyl-cyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-5-[(2-methylphenyl)-4-methylcyclopentadienyl-[c]-tellurophene]zirconium dichloride and methyl;
dimethylsilandiylbis-5-[2-(2,4,6-trimethylphenyl)cyclopentadienyl-[c]-tellurophene]zirconium dichloride and methyl;
dimethylsilandiylbis-5-[2-mesitylenemethylcyclopentadienyl-[c]-tellurophene]zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2,4-diisopropyl-cyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2,4-diter-butyl-cyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
dimethylsilyl-5-(2,4-dimethyl-cyclopentadienyl-[c]-tellurophene)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiylbis-5-(2,4-ditrimethylsilyl-cyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
methylenebis-5-(2-methylcyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
methylenebis-5-(2-isopropylcyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
methylenebis-5-(2-phenylcyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
methylenebis-5-(2,4-dimethyl-cyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
methylenebis-5-[(2-methylphenyl)-4-methylcyclopentadienyl-[c]-thiophene]zirconium dichloride and methyl;
methylenebis-5-[2-(2,4,6-trimethylphenyl)cyclopentadienyl-[c]-thiophene]zirconium dichloride and methyl;
methylenebis-5-[2-mesitylene-4-methylcyclopentadienyl-[c]-thiophene]zirconium dichloride and methyl;
methylenebis-5-[2,4-diisopropyl-cyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
methylenebis-5-(2,4-diter-butyl-cyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
methylenebis-5-(2,4-ditrimethylsilyl-cyclopentadienyl-[c]-thiophene)zirconium dichloride and methyl;
methylenebis-5-(2-methylcyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
methylenebis-5(2-isopropylcyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
methylenebis-5-(2-phenylcyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
methylenebis-5-(2,4-dimethyl-cyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
methylenebis-5-[(2-methylphenyl)-4-methylcyclopentadienyl-[c]-phosphole]zirconium dichloride and methyl;
methylenebis-5-[2-(2,4,6-trimethylphenyl)cyclopentadienyl-[c]-phosphole]zirconium dichloride and methyl;
methylenebis-5-[2-mesitylene-4-methylcyclopentadienyl-[c]-phosphole]zirconium dichloride and methyl;
methylenebis-5-(2,4-diisopropyl-cyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
methylenebis-5-(2,4-diter-butyl-cyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
methylenebis-5-(2,4-ditrimethylsilyl-cyclopentadienyl-[c]-phosphole)zirconium dichloride and methyl;
methylenebis-5-(2-methylcyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
methylenebis-5-(2-isopropylcyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
methylenebis-5-(2-phenylcyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
methylenebis-5-(2,4-dimethyl-cyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
methylenebis-5-[(2-methylphenyl)-4-methylcyclopentadienyl-[c]-tellurophene]zirconium dichloride and methyl;
methylenebis-5-[2-(2,4,6-trimethylphenyl)cyclopentadienyl-[c]-tellurophene]zirconium dichloride and methyl;
methylenebis-5-[2-mesitylene-4-methylcyclopentadienyl-[c]-tellurophene]zirconium dichloride and methyl;
methylenebis-5-(2,4-diisopropyl-cyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
methylenebis-5-(2,4-diter-butyl-cyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
dimethylsilyl-5-(2,4-dimethyl-cyclopentadienyl-[c]-tellurophene)-1-(2-methyl-4-phenylendenyl)zirconium dichloride and methyl;
methylenebis-5-(2,4-ditrimethylsilyl-cyclopentadienyl-[c]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-4-(cyclopentadienyl-[2,1-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-4-(2-methylcyclopentadienyl-[2,1-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-4-(2,5-dimethylcyclopentadienyl-[2,1-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-4-(2,5-diisopropylcyclopentadienyl-[2,1-b]-thiophene)zirconium dichloride and methyl;
dimethylsilandiylbis-4-(2,5-diter-butylcyclopentadienyl-[2,1-b]-thiophenerzirconium dichloride and methyl;
dimethylsilandiylbis-4-(2,5-ditrimethylsilylcyclopentadienyl-[2,1-b]-thiophene)zirconium dichloride and methyl;
dimethylsilyl-4-(2,5-ditrimethylsilylcyclopentadienyl-[2,1-b]-thiophene)-1-(2-methyl-4-phenyl)zirconium dichloride and methyl;
dimethylsilandiylbis-4-(cyclopentadienyl-[2,1-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-4-(2-methylcyclopentadienyl-[2,1-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-4-(2,5-dimethylcyclopentadienyl-[2,1-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-4-(2,5-diisopropylcyclopentadienyl-[2,1-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-4-(2,5-diter-butylcyclopentadienyl-[2,1-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiylbis-4-(2,5-ditrimethylsilylcyclopentadienyl-[2,1-b]-tellurophene)zirconium dichloride and methyl;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)(3-methylcyclopentadienyl)zirconium dichloride and methyl;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)(3-ter-butylcyclopentadienyl)zirconium dichloride and methyl;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)-1-(benzoindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)-1-(benzoindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)-1-(benzoindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-5-(2,4-dimethyl-cyclopentadienyl-[c]-thiophene)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-5-(2,4-dimethyl-cyclopentadienyl-[c]-phosphole)-1-(2-methyl-4-phenylindenylzirconiun dichloride and methyl;
dimethylsilandiyl-5-(2,4-dimethyl-cyclopentadienyl-[c]-thiophene)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-5-(2,4-dimethyl-cyclopentadienyl-[c]-phosphole)-1-(2-methyl-4-phenylindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-5-(2,4-dimethyl-cyclopentadienyl-[c]-phosphole)-1-(benzoindenyl)zirconium dichloride and methyl;
dimethylsilandiyl-4-(2,5-ditrimethylsilylcyclopentadienyl-[2,1-b]-tellurophene)-1-(2-methyl-4-phenyl)zirconium dichloride and methyl.
An interesting class of metallocene compounds according to the present invention is that of formula (I) wherein both Y and Z are a moiety of formula (II), R1 is a C1-C20-alkyl group, preferably a methyl group, R2 is hydrogen, R3 is different from hydrogen, B and D are carbon atoms, A is an element of the group 16 of the Periodic Table of the Elements (new IUPAC version), preferably sulfur, m is 0, n and s are 1. Preferably R3 is a C6-C20-aryl group, such as a phenyl group or a naphthyl group, or a C7-C20-alkylaryl group wherein the alkyl group is ortho-substituted to the aryl substituent, such as an ortho-methylphenyl group or the aryl group is a 2,4 disubstituted phenyl group such as 2,4-dimethyl-phenyl. Preferably It is different from hydrogen. Preferably R5 is a hydrogen.
In this class of metallocenes according to the invention the ring that comprises the heteroatom contains a double bond and thus has an aromatic character.
Non limiting examples of said class are:
dimethylsilandiylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride,
dimethylsilandiylbis-6-(3,5-dimethyl-cyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and
dimethylsilandiylbis-6-[2,5-dimethyl-3-(2xe2x80x2-methylphenylcyclopentadienyl-[1,2-b]-thiophene]zirconium dichloride.
Another particular advantageous class of metallocenes according to the present invention are those wherein both Y and Z are a moiety of formula (II), L is a  greater than C(R17)2 group, R1 is a hydrogen atom, R2 is different from hydrogen.
Non limiting examples of said class are:
isopropylidenebis-6-(4-methylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
isopropylidenebis-6-(4-isopropylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
isopropylidenebis-6-(4-terbutylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
isopropylidenebis-6-(4-phenylclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
methylenebis-6-(4-methylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
methylenebis-6-(4-isopropylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
methylenebis-6-(4-terbutylcyclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl;
methylenebis-6-(4-phenylclopentadienyl-[1,2-b]-thiophene)zirconium dichloride and methyl.
Yet another particular advantageous class of metallocene compound according to the present invention corresponds to formula (I) wherein both Y and Z are a moiety of formula (II), m is 2 and R5 is not hydrogen.
Non limiting examples of said class are:
dimethylsilandiylbis-6-(1,1,2,5-tetramethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
dimethylsilandiylbis-6-(1,1,2,5-tetramethyl-3-phenylcyclopentadienyl-[1,2-b]-cyclopentadien)zirconium dichloride and methyl;
isopropylidenebis-6-(1,1,2,5-tetramethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)zirconium dichloride and methyl;
isopropylidenebis-6-(1,1,2,5-tetramethyl-3-phenylcyclopentadienyl[1,2-b]-cyclopentadien)zirconium dichloride and methyl.
According to another aspect of the present invention it is provided a class of ligands of formula (V): 
wherein Yxe2x80x2 is a moiety of formula (VI): 
wherein R1, R2, R3, R4, R5, A, B, D, n, m and s are defined as described above and the ring containing A, B and D can have double bonds in any of the allowed positions, having an aromatic character;
and/or its double bond isomers;
Zxe2x80x2 is selected from a moiety of formula (VI) and from a moiety of formula (VII): 
and/or its double bond isomers;
R6, R7, R8 and R9 are defined as described above;
when Zxe2x80x2 is equal to Yxe2x80x2, A, B and D in Yxe2x80x2 and Zxe2x80x2 can be the same or different from each other;
L is a divalent bridge as defined above.
Preferably Zxe2x80x2 is equal to Yxe2x80x2; R1 is a C1-C20-alkyl group, preferably a methyl group, R2 is hydrogen, R3 is different from hydrogen, B and D are carbon atoms, A is an element of the group 16 of the Periodic Table of the Elements (new IUPAC version), preferably sulfur, m is 0, n and s are 1.
More preferably R3 is a C6-C20-aryl group, such as a phenyl group or a naphthyl group, or a C7-C20-alkylaryl group wherein the alkyl group is ortho-substituted or ortho and meta-substituted to the aryl substituent, such as an ortho-methylphenyl group or 2-4 methylphenyl group. Preferably R4 is different from hydrogen. Preferably R5 is a hydrogen.
When Zxe2x80x2 is different from Yxe2x80x2 it is preferred a moiety of formula (VIII): 
and/or its double bond isomers;
wherein R11, R12, R13, R14, R15 and R16 are defined as above.
Non limiting examples of said class are:
dimethylbis-6-(3-methylcyclopentadienyl-[1,2-b]-thiophene)silane;
dimethylbis-6-(3-isopropylcyclopentadienyl-[1,2-b]-thiophene)silane;
dimethylbis-6-(3-phenylcyclopentadienyl-[1,2-b]-thiophene)silane;
dimethylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene]silane;
dimethylbis-6-[2,5-dimethyl-3-(2-methylpheny)cyclopentadienyl-[1,2-b]-thiophene]silane;
dimethylbis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-thiophene]silane;
dimethylbis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-thiophene]silane;
dimethylbis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b-]-thiophene)silane;
dimethylbis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)silane;
dimethylbis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)silane;
dimethylbis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)silane;
dimethylbis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)silane;
dimethylbis-6-(3-methylcyclopentadienyl-[1,2-b]-silole)silane;
dimethylbis-6-(3-isopropylcyclopentadienyl-[1,2-b]-silole)silane;
dimethylbis-6-(3-phenylcyclopentadienyl-[1,2-b]-silole)silane;
dimethylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-silolesilane;
dimethylbis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-silole]silane;
dimethylbis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-silole]silane;
dimethylbis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b-silole]silane;
dimethylbis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)silane;
dimethylbis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)silane;
dimethylbis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-silole)silane;
dimethylbis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-silole)silane;
dimethylsilyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-silole)-1-(2-methyl-4-phenylindenyl)silane;
dimethylbis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-silole)silane;
dimethylbis-6-(3-methylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(3-isopropylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-tellurophene]silane;
dimethylbis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-tellurophene]silane;
dimethylbis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-tellurophene]silane;
dimethylbis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(3-methylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(3-isopropylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-tellurophene]silane;
dimethylbis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-tellurophene]silane;
dimethylbis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-tellurophene]silane;
dimethylbis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane; 1dimethylbis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylsilyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)-1-(2-methyl-4-phenylindenyl)silane;
dimethylbis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)silane;
dimethylbis-6-(3-methylcyclopentadienyl-[1,2-b]-phosphole)silane;
dimethylbis-6-(3-isopropylcyclopentadienyl-[1,2-b]-phosphole)silane;
dimethylbis-6-(3-phenylcyclopentadienyl-[1,2-b]-phosphole)silane;
dimethylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)silane;
dimethylbis-6-[2,5-dimethyl-3-(2-methylphenyl)cyclopentadienyl-[1,2-b]-phosphole]silane;
dimethylbis-6-[2,5-dimethyl-3-(2,4,6-trimethylphenyl)cyclopentadienyl-[1,2-b]-phosphole]silane;
dimethylbis-6-[2,5-dimethyl-3-mesitylenecyclopentadienyl-[1,2-b]-phosphole]silane;
dimethylbis-6-(2,4,5-trimethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)silane;
dimethylbis-6-(2,5-diethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)silane;
dimethylbis-6-(2,5-diisopropyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)silane;
dimethylbis-6-(2,5-diter-butyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)silane;
dimethylbis-6-(2,5-ditrimethylsilyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)silane;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)-1-(2-methyl-4-phenylindenyl)silane;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-phosphole)-1-(2-methyl-4-phenylindeneylsilane;
dimethylsilandiyl-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-tellurophene)-1-(2-methyl-4-phenylindenyl)silane.
Most preferably the ligands according to the present invention are
dimethylbis-6-(2,5-dimethyl-3-phenylcyclopentadienyl-[1,2-b]-thiophene)silane;
dimethylbis-6-[2,5-dimethyl-3-(2xe2x80x2-methylphenyl)cyclopentadienyl-[1,2-b]-thiophene]silane;
dimethylbis-6-(3,5-dimethylcyclopentadienyl-[1,2-b]-thiophene)silane.
The aforementioned compounds of formula (V) are particularly useful as intermediate ligands for the preparation of the metallocene compounds of formula (I).
According to a further aspect of the present invention there is provided a process for the preparation of a ligand of formula (V), wherein L, Yxe2x80x2 and Zxe2x80x2 are defined as described above, with the proviso that R2 is a hydrogen and D is a carbon atom, comprising the following steps:
a) contacting a compound of formula (IX) 
wherein the double bonds can be in any of the allowed positions;
A, B, R3, R4, R5, n and m have the meaning as defined above, with a compound of general formula (X): 
wherein R1 has the same meaning as defined above;
In the presence of a ring-closure agent, to obtain the compound of the general formula (XI): 
wherein the double bonds can be in any of the allowed positions;
b) conversion into the compound of formula (XII): 
wherein the double bonds can be in any of the allowed positions; and
when Zxe2x80x2 is equal to Yxe2x80x2, wherein A and B in Yxe2x80x2 and Zxe2x80x2 are the same or different from each other:
c1) treating the compound of formula (XII) with a base selected from hydroxides and hydrides of alkali- and earth-alkali metals, metallic sodium and potassium, and organometallic lithium salts, and subsequently contacting with a compound of formula LQ2 (XIII), wherein L has the same meaning as defined above, and Q is an halogen atom selected from chloride, iodide and bromide preferably bromine, wherein the molar ratio between the compound of formulae (XII) and (XIII) is at least 2;
or when Zxe2x80x2 is a compound of formula (VII):
c2) treating the compound of formula (XII) with a base as defined under c1), and subsequently contacting with a compound of formula Zxe2x80x2LQ (XIV), wherein L has the same meaning as defined above, and Q is a halogen atom selected from chloride, iodide and bromide;
Preferably in the process according to the present invention the ring-closing agent is selected from phosphorus pentoxide-methansulfonic acid (PPMA) and polyphosphoric acid (PPA).
In the process according to the present invention the compound of general formula (X) is selected from xcex1,xcex2-unsaturated acids. Most preferably methacrylic acid is used.
Preferably, in the process according to the present invention the compound of general formula (IX) is 1-methyl-3-bromo-thiophene.
In the process according to the present invention the conversion into the compound of formula (XII) preferably is carried out in the presence of a reduction agent and para-toulene sulfonic acid monohydrate.
In the process according to the present invention the reduction agent is preferably lithium aluminum hydride (LiAlH4).
Non-limiting examples of compounds of formula LQ2 (XIII) are dimethyldichlorosilane, diphenyldichlorosilane, dimethyldichlorogermanium, 2,2-dichloropropane and 1,2-dibromoethane.
Preferably, in the process according to the present invention the compound of formula LQ2 (XIII) is dimethyldichlorosilane.
Non-limiting examples of compounds able to form the anionic compound of formula (XII) are hydroxides and hydrides of alkali- and earth-alkali metals, metallic sodium and potassium, and organometallic lithium salts. Preferably butyllithium is used.
Non-limiting examples of coupling agent used in step a) are Ni, Pd or Pt-based coupling agent. Coupling agents of this kind which are generally used are described in xe2x80x9cComprehensive organic synthesisxe2x80x9d, Eds. B. M. Trost and I. Fleming, Pergamon, Oxford (1991), Vol. 3, Part 1.6, p.241.
Preferably bis(diphenylphosphino)propane)]dichloronickel(II) (Ni(dPPP)) is used.
The synthesis of the above bridged ligands is preferably carried out by adding a solution of an organic lithium compound in an apolar solvent to a solution of the compound (XII) in an aprotic polar solvent. The thus obtained solution containing the compound (XII) in the anionic form is then added to a solution of the compound of formula LQ2 (XIII) in an aprotic polar solvent. The bridged ligand can be finally separated by conventional general known procedures.
Not limitative examples of aprotic polar solvents which can be used in the above process are tetrahydrofurane, dimethoxyethane, diethylether, toluene and dichloromethane. Not limitative examples of apolar solvents suitable for the above process are pentane, hexane and benzene.
During the whole process, the temperature is preferably kept between xe2x88x92180xc2x0 C. and 80xc2x0 C., and more preferably between xe2x88x9220xc2x0 C. and 40xc2x0 C.
A still further aspect of the present invention is a process for the preparation of the metallocene compounds of formula (I), obtainable by contacting a ligand of formula (V) as described above, with a compound capable of forming a corresponding dianionic compound thereof and thereafter with a compound of formula MXp+2, wherein M, X and p have the meanings as defined above.
The compound able to form said dianion is selected from the group consisting of hydroxides and hydrides of alkali- and earth-alkali metals, metallic sodium and potassium, and organometallic lithium salts, and preferably said anion is n-butyllithium.
Non-limiting examples of compounds of formula MXp+2 are titanium tetrachloride, zirconium tetrachloride and hafnium tetrachloride.
More specifically, said bridged ligands are dissolved in an aprotic polar solvent and to the obtained solution is added a solution of an organic lithium compound in an apolar solvent The thus obtained anionic form is separated, dissolved in an aprotic polar solvent and thereafter added to a suspension of the compound MXp+2 in an aprotic polar solvent. At the end of the reaction, the solid product obtained is separated from the reaction mixture by techniques commonly used in the state of the art.
Non limitating examples of aprotic polar solvents suitable for the above reported processes are tetrahydrofurane, dimethoxyethane, diethylether, toluene and dichloromethane. Non limitating examples of apolar solvents suitable for the above process are pentane, hexane and benzene.
During the whole process, the temperature is preferably kept between xe2x88x92180xc2x0 C. and 80xc2x0 C., and more preferably between xe2x88x9220xc2x0 C. and 40xc2x0 C.
When at least one X substituent in the metallocene compound of formula (I) is different from halogen, it is necessary to substitute at least one substituent X in the obtained metallocene with at least another substituent different from halogen. Such a substitution reaction is carried out by methods known in the state of the art. For example, when the substituents X are alkyl groups, the metallocenes can be reacted with alkylmagnesium halides (Grignard reagents) or with lithiumalkyl compounds.
During the whole process, the temperature is preferably kept between xe2x88x92180xc2x0 C. and 80xc2x0 C., and more preferably between xe2x88x9220xc2x0 C. and 40xc2x0 C.
The heterocyclic metallocene compounds of the present invention can conveniently be used as catalyst components for the polymerization of olefins.
Thus, according to a still further aspect of the present invention there is provided a catalyst for the polymerization of olefins, obtainable by contacting:
A) a metallocene compound of formula (I), and
B) an alumoxane and/or a compound capable of forming an alkyl metallocene cation.
The alumoxane used as component (B) can be obtained by reacting water with an organo-aluminum compound of formula HjAlR183xe2x88x92j or HjAlR186xe2x88x92j, where R18 substituents, same or different, are hydrogen atoms, C1-C20-alkyl, C3-C20-cycloalkyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl, optionally containing silicon or germanium atoms with the proviso that at least one R18 is different from halogen, and J ranges from 0 to 1, being also a non-integer number. In this reaction the molar ratio of Al/water is preferably comprised between 1:1 and 100:1.
Preferably the molar ratio between aluminum and the metal of the metallocene is comprised between about 10:1 and about 20000:1, and more preferably between about 100:1 and about 5000:1. Higher aluminum/zirconium molar ratio can be used with good results even if not practical on industrial scale. The alumoxanes used in the catalyst according to the invention are considered to be linear, branched or cyclic compounds containing at least one group of the type: 
wherein the R19 substituents, same or different, are hydrogen atoms, C1-C20-alkyl, C3-C20-cycloalkyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl, optionally containing silicon or germanium atoms, or are a xe2x80x94Oxe2x80x94Al(R19)2 group and, if appropriate, some R19 substituents can be halogen atoms.
In particular, alumoxanes of the formula: 
can be used in the case of linear compounds, wherein n is 0 or an integer from 1 to 40 and the R19 substituents are defined as above, or alumoxanes of the formula: 
can be used in the case of cyclic compounds, wherein n is an integer from 2 to 40 and the R6 substituents are defined as above.
Examples of alumoxanes suitable for use according to the present invention are methylalumoxane (MAO), tetra-(isobutyl)alumoxane (TIBAO), tetra-(2,4,4-trimethyl-pentyl)alumoxane (TIOAO), tetra-(2,3-dimethylbutyl)alumoxane (TDMBAO), tetra-(2,3,3-trimethylbutyl)alumoxane (TIMBAO),
Other interesting alumoxanes are those obtainable by contacting water with an organoaluminum compound described in the international application PCT/EP00/09111 such as tris(2-phenyl-propyl)aluminium, tris[2-(4-fluoro-phenyl)-propyl]aluminium, tris[2-(4-chlorophenyl)-propyl]aluminium, tris[2-(3-isopropyl-phenyl)-propyl]aluminium, tris(2-phenyl-butyl)aluminium, tris(3-methyl-2-phenyl-butyl)aluminium, tris(2-phenyl-pentyl)aluminium, tris[2-(pentafluorophenyl)-propyl]aluminium, tris[2,2-diphenyl-ethyl]aluminium and tris[2-phenyl-2-methyl-propyl]aluminium.
Further particularly interesting cocatalysts are those described in WO 99/21899 in which the alkyl groups have specific branched patterns.
Non-limiting examples of aluminum compounds according to said PCT application are:
tris(2,3,3-trimethyl-butyl)aluminum, tris(2,3-dimethyl-hexyl)aluminum, tris(2,3-dimethyl-butyl)aluminum, tris(2,3-dimethyl-pentyl)aluminum, tris(2,3-dimethyl-heptyl)aluminum, tris(2-methyl-3-ethyl-pentyl)aluminum, tris(2-methyl-3-ethyl-hexyl)aluminum, tris(2-methyl-3-ethyl-heptyl)aluminum, tris(2-methyl-3-propyl-hexyl)aluminum, tris(2-ethyl-3-methyl-butyl)aluminum, tris(2-ethyl-3-methyl-pentyl)aluminum, tris(2,3-diethyl-pentyl)aluminum, tris(2-propyl-3-methyl-butyl)aluminum, tris(2-isopropyl-3-methyl-butyl)aluminum, tris(2-isobutyl-3-methyl-pentyl)aluminum, tris(2,3,3-trimethyl-pentyl)aluminum, tris(2,3,3-trimethyl-hexyl)aluminum, tris(2-ethyl-3,3-dimethyl-butyl)aluminum, tris(2-ethyl-3,3-dimethyl-pentyl)aluminum, tris(2-isopropyl-3,3-dimethyl-butyl)aluminum, tris(2-trimethylsilyl-propyl)aluminum, tris(2-methyl-3-phenyl-butyl)aluminum, tris(2-ethyl-3-phenyl-butyl)aluminum, tris(2,3-dimethyl-3-phenyl-butyl)aluminum, as well as the corresponding compounds wherein one of the hydrocarbyl groups is replaced by an hydrogen atom, and those wherein one or two of the hydrocarbyl groups are replaced by an isobutyl group.
Other interesting aluminum compounds are compounds wherein R18 contains an aryl group such as:
tris(2-phenyl-propyl)aluminium, tris[2-(4-fluoro-phenyl)-propyl]aluminium, tris[2-(4-chloro-phenyl)-propyl]aluminium, tris[2-(3-isopropyl-phenyl)-propyl]aluminium, tris(2-phenyl-butyl)aluminium, tris(3-methyl-2-phenyl-butyl)aluminium, tris(2-phenyl-pentyl)aluminium, tris[2-(pentafluorophenyl)-propyl]aluminium, tris[2,2-diphenyl-ethyl]aluminium and tris[2-phenyl-2-methyl-propyl]aluminium.
Amongst the above aluminum compounds, trimethylaluminium (TMA), triisobutylaluminium (TIBAL), tris(2,4,4-trimethyl-pentyl)aluminum (TIOA), tris(2,3-dimethylbutyl)aluminum (TDMBA) and tris(2,3,3-trimethylbutyl)aluminum (TTMBA) tris(2-phenyl-propyl)aluminium (TPPA), tris[2-(4-fluoro-phenyl)propyl]aluminium (TFPPA) are preferred.
Non limitative examples of compounds able to form a metallocene alkyl cation are compounds of formula D+Exe2x88x92, wherein D+ is a Brxc3x8nsted acid, able to give a proton and to react irreversibly with a substituent X of the metallocene of formula (I) and Exe2x88x92 is a compatible anion, which is able to stabilize the active catalytic species originating from the reaction of the two compounds, and which is sufficiently labile to be able to be removed by an olefinic monomer. Preferably, the anion Vxe2x88x92 comprises one or more boron atoms. More preferably, the anion Vxe2x88x92 is an anion of the formula BAr(xe2x88x92)4, wherein substituents Ar, the same or different from each other, are aryl radicals such as phenyl, pentafluorophenyl, bis(trifluoromethyl)phenyl. Particularly preferred is the tetrakis-pentafluorophenyl borate. Furthermore, compounds of formula BAr3 can be suitably used wherein Ar is a C7-C20 aryl group optionally substituted with heteroatoms.
The catalysts used in the process of the present invention can be also used on inert supports. This is obtained by depositing the metallocene (A), or the product of the reaction of the same with the component (B), or the component (B) and thereafter the metallocene (A), on supports such as for example silica, alumina, styrene-divinylbenzene copolymers, polyethylene or polypropylene.
The solid compound so obtained, in combination with further addition of the alkyl aluminum compound as such or pre-reacted with water, is usefully employed in gas phase polymerisation. Catalysts of the present invention are useful in the homo- and copolymerization reaction of olefins. Therefore, a still further object of the present invention is a process for the polymerization of one or more olefins comprising the polymerization reaction of one or more olefinic monomer in the presence of a catalyst as above described.
The catalysts of the present invention can be used in the homo-polymerisation reaction of olefins, such as ethylene for the preparation of HDPE, or of alpha-olefins, such as propylene and 1-butene. Particular interesting results are achieved in the polymerisation of propylene carried out in the presence of the above-described catalyst containing the metallocene of the present invention.
It has been found that when the polymerization of propylene is carried out in the presence of the metallocene compounds of the present, the molecular weight of the obtained propylene polymers are unexpectedly high. The intrinsic viscosity (I.V.) of the obtained polypropylene is generally higher than 0.5 dL/g preferably 1 dL/g and can reach values as high as 5 dL/g or even higher.
The obtained propylene polymers are characterized by high isotacticity values. Thus the amount of sequences mrrm (in mol %) is extremely low. In generally the amount of sequences mrrm (in mol %) is lower than 1, preferably lower than 0.5.
When the polymerization of propylene is carried out in the presence of the metallocene compounds of the present invention the melting point of the obtained polypropylene is considerably high. In generally the melting point of the obtained polypropylene is higher than 145xc2x0 C. and can reach values of 160xc2x0 C. or even higher.
Particularly interesting results are obtained when the catalyst of the present invention, in particular when both Y and Z belong to formula (II) and R3 is C6-C20 aryl C7-C20 alkyl aryl or C7-C20 arylalkyl, is used in conjunction with compounds able to form a metallocene alkyl cation of formula T+Vxe2x88x92 wherein T and V are described above. With these cocatalyst is possible to obtain highly isospecific polymers with very low regio-error contents.
A still further advantageous characteristic of the metallocenes of the invention is that the use of a small amount of hydrogen, besides regulating the molecular weight, entails a considerable increase of the polymerization activities.
The catalysts according to the present invention can be used also in a process as described above for the copolymerization of propylene with one or more alpha-olefins such as for example ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-esadecene, 1-octadecene, 1-eicosene, allylcyclohexene, cyclopentene, styrene, cyclohexene, norbornene and 4,6-dimethyl-1-heptene. Copolymers propylene/ethylene and propylene/1-butene are preferred. When 1-butene is used as comonomer, copolymers with relatively high molecular weight but relatively low melting point are obtained.
In the propylene/ethylene copolymers the addition of ethylene strongly reduces the molecular weight of the copolymers, that means that ethylene can be used as molecular weight regulating as well.
Another interesting use of the catalysts according to the present invention is in the copolymerization of ethylene with higher olefins. In particular, the catalysts of the invention can be used for the preparation of LLDPE.
Suitable olefins to be used as comonomers comprise a-olefins of the formula CH2xe2x95x90CHR20, wherein R20 is an alkyl radical having from 1 to 10 carbon atoms or an aryl radical having from 6 to 20 carbon atoms, and cycloolefins. Examples of these olefins are propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-esadecene, 1-octadecene, 1-eicosene, allylcyclohexene, cyclopentene, styrene, cyclohexene, norbornene and 4,6-dimethyl-1-heptene.
The copolymers may also contain small proportions of units deriving from polyenes, in particular from straight or cyclic, conjugated or non conjugated dienes, such as 1,4-hexadiene, isoprene, 1,3-butadiene, 1,5-hexadiene and 1,6-heptadiene.
The units deriving from xcex1-olefins of formula CH2xe2x95x90CHR2, R20 is an alkyl radical having from 1 to 10 carbon atoms or an aryl radical having from 6 to 20 carbon atoms, from cycloolefins and/or from polienes are present in the copolymers preferably in amounts ranging from 1% to 20% by mole.
The saturated elastomeric copolymers can contain ethylene units and xcex1-olefins and/or non conjugated diolefins able to cyclopolymerise. The unsaturated elastomeric copolymers can contain, together with the units deriving from the polymerisation of ethylene and xcex1-olefins, also small proportions of unsaturated units deriving from the copolymerization of one or more polyenes. The content of unsaturated units is preferably comprised between 0 and 5% by weight.
Non limitative examples of suitable xcex1-olefins comprise propylene, 1-butene and 4-methyl-1-pentene. Suitable non conjugated diolefins able to cyclopolymerise comprise 1,5-hexadiene, 1,6-heptadiene and 2-methyl-1,5-hexadiene.
Non limitative examples of suitable polyenes are:
(i) polyenes able to give unsaturated units, such as:
linear, non-conjugated dienes, such as 1,4-hexadiene trans, 1,4-hexadiene cis, 6-methyl-1,5-heptadiene, 3,7-dimethyl-1,6-octadiene and 11-methyl-1,10-dodecadiene;
bicyclic diolefins, such as 4,5,8,9-tetrahydroindene and 6 and 7-methyl-4,5,8,9-tetrahydroindene;
alkenyl or alkyliden norbornenes, such as 5-ethyliden-2-norbornene, 5-isopropyliden-2-norbornene and exo-5-isopropenyl-2-norbornene;
polycyclic diolefins, such as dicyclopentadiene, tricyclo-[6.2.1.02.7]4,9-undecadiene and the 4-methyl derivative thereof;
(ii) non-conjugated diolefins able to cyclopolymerise, such as 1.5-hexadiene, 1,6-heptadiene and 2-methyl-1,5-hexadiene;
(iii) conjugated dienes, such as butadiene and isoprene.
A further interesting use of the catalyst of the present invention is for the preparation of 1-butene homopolymer.
A further interesting use of the catalysts according to the present invention is for the preparation of cycloolefin polymers. Monocyclic and polycyclic olefin monomers can be either homopolymerised or copolymerised, also with linear olefin monomers.
Polymerisation processes according to the present invention can be carried out in gaseous phase or in liquid phase, optionally in the presence of an inert hydrocarbon solvent either aromatic (such as toluene), or aliphatic (such as propane, hexane, heptane, isobutane and cyclohexane).
The polymerisation temperature generally ranges from about 0xc2x0 C. to about 250xc2x0 C. In particular, in the processes for the polymerization of propylene, it is generally comprised between 20xc2x0 C. and 150xc2x0 C., preferably between 40xc2x0 C. and 90xc2x0 C.
The polymerization pressure is ranging from 0,5 to 100 bar, preferably from 2 to 50 bar, and more preferably from 4 to 30 bar.
The molecular weight of the polymers can be also varied merely by varying the polymerization temperature, the type or the concentration of the catalytic components or by using molecular weight regulators such as, for example, hydrogen.
The molecular weight distribution can be varied by using mixtures of different metallocenes, or carrying out the polymerization in several steps at different polymerization temperatures and/or different concentrations of the molecular weight regulator.
The polymerization yields depend on the purity of the metallocene component of the catalyst. Therefore, in order to increase the yields of polymerization, metallocenes are generally used after a purification treatment.
The components of the catalyst can be brought into contact before the polymerization. The pre-contact concentrations are generally between 1 and 10xe2x88x928 mol/l for the metallocene component (A), while they are generally between 10 and 10xe2x88x928 mol/l for the component (B). The pre-contact is generally effected in the presence of a hydrocarbon solvent and, if appropriate, of small quantities of monomer. The pre-contact time is generally comprised between 1 minute and 24 hours.